Gastric Physiology

Question 1

Swalloing

Answer 1

UOsphincter- relaxed food passes through, 5s peristalsis-> stomach via LO sphincter.
Swolloing centre in medulla - somatic nerves- skeletal muscle and autonomic nerves- smooth muscle.
Sphinvters and peristalsis controlled by vagus and enteric nerve plexuses.
Stimach empty: 50mL, full :4L
Pepsinogens converted to pepsins by HCL
Parietal: 2L per day

Question 2

Acid secretion

Answer 2

Exchange of intracellular H+ for extracellular K+ using ATP breakdown energy.
Achieved by proton pump or H+-K+-ATPase protein.
No self digestion of gastric mucosa due to alkaline mucus.

Food in stomach:
Postganglionic parasympathetic fibers in Myenteric plexus release ACh and stimulate release of juices.
Vagal stimulation- G cells gastrin–> blood, gastric glands–> stimulates acid and pepsinogens.
Vagal activity + gastrin –> H2 from Mast cells –> parietal cells -> more HCL.
Arrives at stomach food: gastric phase - 1. Distention and chemiacls.
Then mechanoreceptors streched- ACh- Gastrin, histamine -> acid, enzymes and mucus.

Vagus stimulation- also gatrin releasing peptide (GRP) - acts on G cells to release gastrin.

Low acid inhibits acid secretion, so empty stomach no.

Question 3

Phases of digestion

Answer 3

Gastric- 3 hrs--> chyme
1. Duodenal distenion
2. Prescence of fats
3. Decrease in PH in duodenal lumen 
‼️  inhibition of gastric emprtying- rate appropriate.

Question 4

What is the gastric pit made of?

Answer 4

G cell- gastrin
Chief cell- pepsinogen 
Parietal- intrinsic f (B12 abs and HCL) 
Mucus neck cells
Epithelial cells- secrete HCO3-